About This Tool
The Ratio Calculator solves proportions by finding the missing value in an a:b = c:d relationship. Enter any three of the four values and the calculator determines the fourth using cross-multiplication.
Proportions and ratios appear everywhere — recipe scaling, map distances, architectural plans, mixing solutions, and financial analysis all rely on proportional reasoning. Rather than doing the cross-multiplication manually, this tool gives you the answer instantly and shows the work.
The calculator also simplifies ratios to their lowest terms using the greatest common divisor. Enter 12:18 and it tells you the simplified form is 2:3. This feature is especially useful in cooking, where you often need to scale recipes up or down by a clean ratio.